So I have been undermining for about 6 weeks now at rating 5. I am just about ready to stop. The 50 million per week is nice but after 4-5 hours of killing the enemy I have nothing left in the tank. I wonder why ED does not do something with the cargo that is tossed out by the enemy power? It would make it a little interesting if we could gather it and sell it back for merits. Right now they eject it and it means absolutely nothing....I can see now why a lot of folks have been posting that power play is basically dead.
The piracy bit only works within superpowers. E.g. if you're pledged to Hudson, you can pirate the merits dropped by Winters' ships.
Keep in mind, though, that it's a 1:1 ratio, and you get 30 merits for killing a ship. The time required to pick up 30 dropped items is colossal compared to the time it takes to kill one single ship, and in the end up can't carry more than, AT MOST, 792 merits.
It used to be that you could pirate players quite effectively (again within the same superpower), but that was used to effectively cheat in terms of undermining and just generating credits out of thin air, so it was reduced down to 1:1 instead.
So You get 1 merit for each container of the enemy power you pick up? I didn't know that but you are right, that still is not worth messing with...
It was never really effective for its intended purpose, and ended up being used for either sabotage or management of systems and command capital between powers — both unintended uses. Perhaps this mechanic will be revisited again post 2.4.